linux-kernel - Re: [PATCH 15/60] block: loop: comment on direct access to bvec table

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Message-ID: <CACVXFVPE5BMBS-qwgRDxiab9s=SQGYay0VWhU+SGU8Z390hp7g@mail.gmail.com>
Date:   Tue, 1 Nov 2016 07:08:24 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Jens Axboe <axboe@...com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Hannes Reinecke <hare@...e.com>,
        Mike Christie <mchristi@...hat.com>,
        Minfei Huang <mnghuan@...il.com>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH 15/60] block: loop: comment on direct access to bvec table

On Mon, Oct 31, 2016 at 11:31 PM, Christoph Hellwig <hch@...radead.org> wrote:
> Btw, the lib/iov_iter.c code that iterates over bvec currently
> expects single-page segments.  Is the loop code fine with that?

lib/iov_iter.c has switched to bvec iterator already in the mp-bvec
preparing patchset, so every thing will be fine after multipage bvec
is enabled.

Another multipage bvec benefit for lib/iov_iter.c(dio) is that we
can return whole pages in one segment, instead of one page
each time, such as iov_iter_get_pages(), but that can be
a follow-up optimization.

> Even if it is I think we'd be much better off if it becomes multipage
> segment aware.

This patch is for auditing possible effect with multipage bvec, so
looks we should expose as much as possible direct access to
bvec table.

Thanks,
Ming Lei